Pollution control devices such as catalytic converters and other exhaust gas devices are well known and conventionally used to filter and/or purify the exhaust gases produced by internal combustion engines. Because these devices are subjected to relatively high temperatures during operation, it is necessary that they be sufficiently insulated to limit heat dissipation and/or damage to nearby components.
The most common of these devices include a filtration housing having inlet and outlet connections, with the inlet and outlet connections typically being formed as frusto-conical-shaped assemblies that are double-walled and have an insulating material, in mat form, installed between the two walls. The insulating material must be formed of a material that can withstand the anticipated high operating temperatures and repeated thermal cycles of heatup and cool down without physically or chemically degrading.
Heretofore, the insulating materials used in these pollution control devices have been produced in several ways: (1) they have been formed into insulating mats from slurries of inorganic materials; (2) flat sheets of high temperature resistant insulating material have been die cut to approximate shapes and crudely stuffed into double-walled inlet and outlet assemblies, or (3) flat sheets of materials have been cut and preformed into a desired freestanding shape. In the latter case, retaining elements such as tapes or films are necessary to maintain the preformed shape of the insulation prior to installation. Alternatively, chemical binders such as adhesive mixtures are added to the sheet material so that the insulation will retain a freestanding, preformed shape after an appropriate heat or curing treatment. Each of these prior techniques, however, suffer from one or more of the difficulties of handling and forming, poor fit and/or buckling of the insulation when installed, and/or high materials costs where retaining elements, binders, and the like must be employed during the manufacturing process. Also, organic binders degrade or heat up creating outgassing and concerns for health and safety.